The disclosed embodiments of the present invention relate to wireless communication signal reception, and more particularly, to a wireless communication receiver with phase noise estimation and phase noise compensation performed after channel estimation, and related wireless communication receiving method and phase noise compensation apparatus.
An orthogonal frequency division multiplexing (OFDM) technique distributes the data over a large number of sub-carriers that are spaced apart at defined frequencies. This spacing provides the orthogonality of the OFDM approach, and prevents the demodulators from seeing frequencies other than their own. The benefits of OFDM include high spectral efficiency, resiliency to radio-frequency (RF) interference, and lower multipath distortion. To transmit the signal up to the RF at the transmitter and to shift the received RF signal down to the intermediate-frequency (IF)/baseband at the receiver, practical oscillators are used. However, the practical oscillator generally does not behave in an ideal manner, and thus suffers from phase noise which is a random perturbation of the phase of a steady sinusoidal waveform. Besides, the phase noise of the practical oscillators will be imparted to the signals during the up-conversion at the transmitter and the down-conversion at the receiver. The resulting phase noise spectrum of such a frequency-shifting oscillator is a function of the properties of a free-running oscillator together with those of the components of the phase-locked loop (PLL).
The undesired phase noise introduced from the local oscillator threatens orthogonality of sub-carriers used in an OFDM system. Two effects of phase noise added to the signal by a receiver local oscillator are distinguished as a low-frequency phase noise (typically termed common phase error) and a high-frequency phase noise (typically termed inter-carrier interference). Specifically, the common phase error arises predominantly from the low-frequency components of the phase noise spectrum, and causes a rotation of the signal constellation. Regarding the inter-carrier interference, it corresponds to the summation of the information of the other sub-carriers each multiplied by some complex number which comes from an average of phase noise with a spectral shift, and appears as additive Gaussian noise to the receiver.
As mentioned above, the phase noise introduced by the practical oscillator is unavoidable. However, if the receiver has suitable ability to tackle the effects of phase noise, this can allow the system and RF engineer to relax the specification of the local oscillator used in the receiver.